Our purpose is to investigate the roles of fibronectin and heparin in phagocytosis of gelatin-coated neutral colliods. We are using 125I-gelatin coated latex particles (g-Ltx) in conjunction with rat peritoneal macrophages. Our major aims for the next period are: 1) To establish the important kinetic parameters involved in the phagocytosis of g-Ltx. 2) To study the involvement of fibronectin in the phagocytosis of tissue debris and determining factors. 3) To investigate the nature of macrophage receptors in relationship to Fc and C3b receptors. 4) To study the nature and role of phosphorylation of chicken surface fibronectin from fibroblast by protein kinases.